Rock lobsters are found in the Waterbirth Island Dungeon's fifth sub-level, in room 16. They are similar to giant rock crabs in the fact that they are initially disguised as large rocks, but they will attack the player as they approach. They have very high defence (though they are weak to magic attacks) and can hit frequently into the low 300s. They attack every other game tick, making them incredibly dangerous especially if multiple lobsters attack at once. Rock lobsters are commonly killed by wealthy players because of their common crimson charm drops. Using the right technique, such as ice bursting or ice barraging, killing rock lobsters is one of the fastest ways of obtaining charms.

The rock lobster's combat level was 127 upon being introduced into RuneScape 2. It was later changed to 156 in a hidden update. Their combat levels changed again to 142 upon the release of the Evolution of Combat on 20 November2012.